Among the different types of proteins embedded in the cellular membrane, integrins link the cytoskeleton to the extracelular matrix and play a central role in a variety of signaling processes. The general mechanism of integrin regulation, which is based on an interdomain hinging motion between two states, has been implicated in processes including cell migration, adhesion, and internal signaling. To understand the fundamental nature of these cellular functions, this proposal describes investigations to determine the mechanical properties of this conformational motion at the single molecule level. The molecular underpinnings of the conformational changes in integrins are especially suited to investigation by optical tweezers and single molecule fluorescence spectroscopies, as the small forces and displacements .that are accessible with these techniques are in the range of those of interdomain motions in integrins. The proposed research will resolve the molecular substates of the integrin regulation mechanism in single immobilized proteins, yielding results that will provide the foundation for additional exploration of the extended signaling cascade, including direct interrogation of integrin mediated transmembrane signaling. [unreadable] [unreadable]